where \(g\)  must be a function of \(f\)  and \(h\) . In [1]}, the following transformation is advocated:
\(g = \left(\mathcal {I}^B_C\right)^{-1}( \mathcal {I}^A_C(h) \cdot \mathcal {I}^B_A(f) ).\) 
